The present invention relates to rotating searchlights and, more particularly, to drive mechanisms as employed therewith to cause the searchlight to rotate in an oscillating fashion.
Carbon-arc-type searchlights are well known to the general public in association with outdoor advertising. At night-time events at which it is desired to draw attention to a particular location from over a large viewing area, it is common to place a number of carbon-arc searchlights at the location and face them skyward. The lamps are then rotated causing a decorative and attention-getting pattern of light beams in the sky emanating from the location to which it is desired to draw attention. Such searchlights have been around for years, with the last actual construction thereof taking place somewhere around 1946.
Recently, the availability of high-intensity lamps has caused the construction of newer searchlight assemblies for use in such advertising making use of the technology which has been developed in the interim 35 years since the last carbon-arc searchlights were constructed. Such a unit as built by the applicant herein is shown in FIG. 1. As can be seen from the sequence displayed therein, the searchlight assembly, generally indicated as 10, comprises a base 12 which includes the necessary power supplies (not shown). A turret 14 is mounted on base 12 for rotation about an axis. One or more searchlights 16 containing high intensity lamps are mounted to the turret 14 for rotation therewith. As the turret 14 rotates in the horizontal plane about its vertical axis, the searchlights 16 are simultaneously and in unison rotated up and down in vertical planes giving the appearance of three light beams converging and then fanning out in a perfect pattern.
The high intensity lamps must have a constant power source connected thereto, as a momentary interruption will cause the lamp to be extinguished. Moreover, the power source is a high amperage D.C. current. Accordingly, it is not possible to rotate the turret 14 constantly in one direction with electric power supplied to the searchlights 14 through a slip-ring arrangement. Rather, a solid cable must be run from the searchlights 16 and the rotating turret 14 to the power supply contained within base 12. Accordingly, turret 14 must be rotated in an oscillating fashion.
In attempting to drive turret 14 in an oscillating manner, the applicant herein found that conventional drive mechanisms were either initially inoperative or soon failed. The turret 14 has a high mass and, therefore, a high inertia. By affixing a large ring gear to the turret, the turret could be driven by a spur gear engaged thereto being driven by a motor. By constantly reversing the motor, however, the high inertial forces soon caused the motor to burn out. Stepping motors, as tried, had their own set of problems, not the least of which was the high cost of the motor itself.
Wherefore, it is the object of the present invention to provide a drive mechanism for driving the turret of such searchlight assemblies in a smoothly oscillating manner with a mechanism having a low initial cost, high reliability, and long life expectancy.